Modern motor vehicles often comprise an electric parking brake. This can be operated by the driver by means of a control switch that is connected to an electronic controller, which controls one common or two separate parking brake actuators for two wheels. For safety reasons, it is desirable that the electric parking brake operates reliably even in the event of single faults occurring.
An electromechanical parking brake system for motor vehicles is known from DE 197 51 431 A1, which comprises a brake actuating device, an electronic controller for the conversion of input signals into corresponding output signals, and two motor operated parking brakes, which can be controlled depending on output signals of the controller. In order to increase operational reliability, the electronic controller comprises two or a plurality of parallel control units for the separate processing of the input signals. Thus in the event of a defect in one of the branches, at least one parking brake can still be operated. Preferably, a backup battery for the supply of the control units and the parking brakes can be switched on by means of an additional switch. In vehicles having automatic gearboxes it is provided to use the parking lock in the gearbox to hold the vehicle instead of a backup battery in the event of an electrical fault.
Also typical vehicles having manual transmissions can ensure adequate parking on a gradient by engaging a suitable gear, which acts as a second redundant means of preventing the vehicle from rolling away besides the parking brake.
Vehicles driven by electric motors can comprise a gearbox; on the other hand there is often no gearbox because electric drives can cover a large range of revolution rates and hence a wide speed range even without gearboxes. Furthermore, modern internal combustion engines and gearboxes are frequently designed with low friction in such a way that self-locking, which would allow parking on a hill with a gear engaged, is not guaranteed. Such versions of vehicles also require a safe redundant rollaway prevention means on a hill.
A parking brake system for motor vehicles is known From DE 10 2007 029 632 A1 having a control element and at least two electromechanical actuators, each for the generation of a parking brake force on a wheel of the motor vehicle, in which the electromechanical actuators are each provided with a wheel electronic means and wherein the control element is connected by means of a control unit to the wheel electronic means of the first electromechanical actuator via a first signal line and via a second signal line by means of a further control unit to the wheel electronic means of the second electromechanical actuator. Furthermore, at least a third signal line is provided, which directly connects the control element to the wheel electronic means or to one of the electromechanical actuators respectively and transmits the driver's demand. Preferably, the third signal line is designed in such a way that it connects the control element directly to the wheel electronic means of the electromechanical actuators on the one hand and on the other hand connects the two wheel electronic means to each other and enables communications between the wheel electronic means. It is preferred if a redundant power supply is provided for the parking brake system. This ensures parking of the vehicle with a safeguard against single faults, although the parking brake system is complex and thus expensive.
The object of the present invention is to provide an alternative electric parking brake that enables fail-safe parking of the vehicle on a gradient.
This object is achieved through an electronic controller as described herein (in conjunction with a conventional control element and conventional parking brake actuators) as well as a related brake system.